The present invention relates to expansion joints and, more particularly, to high temperature, non-metallic expansion joints for use in a high heat rate environment in ducts carrying gases.
Expansion joints are needed in ducts carrying high temperature gases. The demands on the expansion joints are greater where the high temperature gases are characterized by high turbulence, fast heat rate, high gas flow rate, or any combination of these, and/or where large movements and high cycles of movement are required of the expansion joint. These conditions can exist in cogeneration facilities for generating electricity and/or steam, gas transmission pump stations, power peaking plants, dryers and gas turbine engine test stands.
The frames associated with known non-metallic expansion joints for use under these conditions experience cracking as a result of 1) high heat rates, 2) high temperature differentials across the frame, and 3) high localized stresses, primarily in welds attaching liners, or sleeves, to the rest of the expansion joint. The liners are made of plates adjacent to and parallel to the flowing high temperature gases and surrounding the flowing gases. As a result of this configuration, the liners heat quickly and tend to expand quickly as a result of the fast temperature rise. However, they are welded to members of the expansion joint which extend away from the hot gases and, therefore, heat and expand more slowly than the liners. Consequently, high stresses occur in the welds attaching the liners to the other members, leading to failures in the expansion joint at the welds.
Furthermore, some prior art frames include members which extend perpendicular to the flowpath of the gases all the way from an inner side of the frame to the outer side of the frame. Such members are particularly unable to accommodate expansion from the thermal shock from the start-up of, for example, a gas turbine, as well as the contraction due to the thermal shock of shutting down the turbine. In addition, poor frame configuration and insulation schemes have led to premature failure of the non-metallic expansion joint components.